An antenna arrangement is already known from U.S. Pat. No. 4,647,937, which comprises a first antenna loop to the radio frequency, and an amplifier for the received signal. A second antenna loop is furthermore provided, which comprises a second adjustable capacitor, wherein the first adjustable capacitor and the second adjustable capacitor can be set by means of a common actuating element. The first antenna loop is connected via the amplifier with a selector switch. The second antenna loop is directly connected via feed lines with the selector switch. By means of the selector switch either the output of the amplifier or the feed line of the second antenna loop can be connected with an output connector. Depending on the reception quality of the radio waves, the first antenna loop is connected via the amplifier with the output connector, or the second antenna loop via the feed line.
An antenna for a radio receiver is known from U.S. Pat. No. 4,625,212, which comprises a capacitively tunable loop.
An automatic tuning system for an antenna is known from U.S. Pat. No. 5,225,847, which contains a single adjustable reactance element. The output which is transmitted to the antenna, and the output which is reflected from the antenna to a feed line, are measured. A feed loop is provided, which is connected via the feed line with a transmitter/receiver. The transmitter/receiver can be operated in a transmitting mode or a receiving mode. In the transmitting mode the transmitter/receiver transmits a signal which is to be radiated by the antenna, to the feed loop.
A loop antenna is known from FR 2 636 781, which is intended to radiate a first signal and to receive a second signal as an echo. The loop antenna includes a pair of connecting terminals which is used for feeding in the first signal as well as for removing the second signal.
The invention relates to an antenna arrangement for transmitting and receiving radio signals.
A radio transmitting/receiving device is known from DE-OS 2 362 889, which has a circuit arrangement for the contactless selective connection of the antenna with the receiver or the transmitter. The circuit arrangement consists of controllable impedance networks respectively located between the antenna and the transmitter and between the antenna and the receiver, which are permeable for the operating frequency band, and of electronic switches assigned to the impedance networks. The critical frequency of the impedance network is electrically changed by the actuation of the electronic switch in such a way that the impedance network becomes impermeable to the operating frequency.